1. Field of the Invention
The present invention relates to a filter excessive temperature rise restricting method for restricting an excessive temperature rise of a filter in an internal combustion engine equipped with the filter for collecting particulate matter contained in the exhaust gas provided in the exhaust passage.
2. Description of the Related Art
Internal combustion engines having a filter provided in the exhaust passage to collect particulate matter such as soot contained in the exhaust gas are known. In the internal combustion engine having a filter, a filter regeneration process is performed when the amount of the particulate matter depositing on the filter becomes equal to or larger than a specified amount. In the filter regeneration process, the temperature of the filter is raised to oxidize and remove the particulate matter depositing on the filter.
In the filter regeneration process, there is a risk that the temperature of the filter can be raised excessively by the heat generated by oxidation of the particulate matter, so that heat deterioration of the filter can be accelerated or the filter can be melted. In view of this, there is a known technology in which fuel injection in the form of post injection is regulated based on the flow quantity of the exhaust gas to control the oxygen concentration in the exhaust gas, thereby restricting an excessive temperature rise of the filter (see, for example, Japanese Patent Application Laid-Open No. 2002-285897). There is another known technology in which when the temperature of the filter is high and the oxygen concentration in the exhaust gas is high at the time when the running state of an internal combustion engine shifts from high load running to idle running, the oxygen concentration in the exhaust gas is reduced, thereby restricting an excessive temperature rise of the filter (see, for example, Japanese Patent Publication No. 5-11205). There is still another known technology in which when an internal combustion engine comes to a running state that requires restriction of autoignition of the particulate matter depositing on the filter, fuel injection quantity in pilot injection is increased, thereby restricting an excessive temperature rise of the filter (see, for example, Japanese Patent Application Laid-Open No. 2003-172124).
As described in the above, in the internal combustion engine equipped with a filter for collecting particulate matter contained in the exhaust gas provided in the exhaust passage, when the risk of an excessive temperature rise of the filter becomes high during the filter regeneration process, the oxygen concentration in the exhaust gas is reduced to suppress oxidation of the particulate matter, thereby restricting an excessive temperature rise of the filter.
In that case, while the oxygen concentration in the exhaust gas is made low, removal of the particulate matter from the filter hardly proceeds. Consequently, after reducing the oxygen concentration in the exhaust gas, even in the case that the possibility of an excessive temperature rise has been made low, a steep increase in the oxygen concentration can bring about an excessive temperature rise of the filter due to rapid oxidation of the particulate matter remaining on the filter without being removed.